Method and arrangement for power control

ABSTRACT

A method for setting a power control level ( 600 ) in a wireless communication system. The method includes the steps of obtaining ( 620 ) transmission information from a wireless subscriber unit, and modifying a power control level and/or a communication channel format ( 660 ) in response to said transmission information. Preferably, the transmission information is re-transmission requests from a wireless subscriber unit, which are transmitted frequently. In this manner, rapid adjustment of power control can be attained utilising an optimal selection of the available communication channel format, followed by a fine-tuning power control operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/309,498 (allowed), filed Dec. 4, 2002, which claims the benefit ofUnited Kingdom Application GB 129098.0 filed Dec. 5, 2001. The contentsof these patent applications are incorporated by reference herein intheir entirety.

FIELD OF THE INVENTION

This invention relates to power control in a wireless communicationsystem. The invention is applicable to, but not limited to, closed-looppower control in a UMTS terrestrial radio access (UTRA) time divisionduplex (TDD), code division multiple access (CDMA) communication system.

BACKGROUND OF THE INVENTION

Wireless communication systems, for example cellular telephony orprivate mobile radio communication systems, typically provide for radiotelecommunication links to be arranged between a plurality of basetransceiver stations (BTS), referred to as Node Bs with regard touniversal mobile telecommunication system (UMTS) systems, and aplurality of subscriber units, often referred to as user equipment (UE)in UMTS systems.

The communication link from a Node B to a UE is generally referred to asa down-link communication channel. Conversely, the communication linkfrom a UE to a Node B is generally referred to as an up-linkcommunication channel.

In an UTRA-based wireless communication system, each Node B hasassociated with it a particular geographical coverage area (or cell).The coverage area is defined by a particular range over which the Node Bcan maintain acceptable communications with UEs operating within itsserving cell. Often these cells combine to produce an extensive coveragearea.

In such wireless communication systems, methods exist for communicatinginformation simultaneously where communication resources in acommunication network are shared by a number of users. Such methods aretermed multiple access techniques. A number of multiple accesstechniques exist, whereby a finite communication resource is dividedinto any number of physical parameters, such as:

-   -   (i) Frequency division multiple access (FDMA) whereby        frequencies used in the communication system are shared,    -   (ii) Time division multiple access (TDMA) whereby each frequency        used in the communication system, is shared amongst users by        dividing the communication resource (each frequency) into a        number of distinct time periods (time-slots, frames, etc.), and    -   (iii) Code division multiple access (CDMA) whereby communication        is performed by using all of the respective frequencies, in all        of the time periods, and the resource is shared by allocating        each communication a particular code, to differentiate desired        signals from undesired signals.

Within such multiple access techniques, different duplex (substantiallysimultaneous two-way communication) paths are arranged. Such paths canbe arranged in a frequency division duplex (FDD) configuration, wherebya first frequency is dedicated for up-link communication and a secondfrequency is dedicated for down-link communication.

Alternatively, the paths can be arranged in a time division duplex (TDD)configuration, whereby a first time period is dedicated for up-linkcommunication and a second time period is dedicated for down-linkcommunication within the same frequency channel. In addition, somecommunication channels are used for carrying traffic and other channelsare used for transferring control information, such as call paging,between the base station and the subscriber units.

Wireless communication systems are distinguished over fixedcommunication systems, such as the public switched telephone network(PSTN), principally in that mobile stations/subscriber equipment movebetween coverage areas served by different Node B (and/or differentservice providers). In doing so, the mobile stations/subscriberequipment encounter varying radio propagation environments. Inparticular, in a mobile context, a received signal level can varyrapidly due to multipath and fading effects.

The present invention will be described with respect to the 3^(rd)Generation Partnership Project (3GPP) technical specification ‘TS25.224’for a wireless communication system based on the universal mobiletelecommunications standard (UMTS). UMTS is a CDMA-based system. A CDMAsystem employs spread spectrum signaling. Two categories of spreadspectrum communications are direct sequence spread spectrum (DSSS) andfrequency hopping spread spectrum (FHSS).

In the case of a DSSS communication system, for example, the spectrum ofa signal can be most easily spread by multiplying it with a wide-bandpseudo-random code generated signal. It is essential that the spreadingsignal be precisely known so that the receiver can de-spread the signal.A cellular communication system using DSSS is commonly known as a DirectSequence Code Division Multiple Access (DS-CDMA) system, one example ofwhich is defined in the TIA-EAI standard IS95.

Individual users in the system use the same radio frequencies and timeslots, but they are distinguishable from each other by the use ofindividual spreading codes. Hence, multiple communications channels areallocated using a number of spreading codes within a portion of theradio spectrum. Each unique code is assigned to a UE, except for commonchannels.

One feature associated with most wireless communication systems, whichis particularly needed in a UTRA system, allows the transceivers in theNode B and UE to adjust their transmitter output power to take intoaccount the geographical distance between them. The closer the UE is tothe Node B's transceiver, the less power the UE and the Node B'stransceivers are required to transmit, for the transmitted signal to beadequately received by the other communication unit. This ‘powercontrol’ feature saves battery power in the UE and also helps to reducethe level of potential interference within the communication system.Initial power settings for the UE, along with other control information,are set by the information provided on a beacon physical channel for aparticular cell.

The 3GPP specification assumes a downlink shared channel (DSCH) callmodel that allows for the implementation of slowmeasurement-report-based power control of Physical Downlink (DL) SharedChannels (PDSCH's). In such a scheme, the user equipment (UE) isrequested to send sporadically measurement reports from which thecurrent mean pathloss between node-B and UE may be determined. Inaddition, the UE may send interference power measurements. This DL powercontrol scheme is termed “slow” due to the delay in the UE making themeasurement and conveying this to the RNC entity via the node-B and dueto the measurement reports being sent every few seconds. Measurementreports are sent in gaps between radio link control (RLC) messages thatare typically used by a UE to request re-transmission of information(data packets) received in error. This is in contrast with fast (frameor sub-frame) based power control typically applied to dedicateddownlink physical channels (DPCHs).

It is known that accurate power control is a vital element of CDMAsystems as the spreading codes are not orthogonal on the reverse link.Hence, any error in the power control (PC) levels introducesinterference that directly reduces system capacity.

Furthermore, it is known that the 3GPP standard is particularlysensitive to power control mismatches in the up-link because of fastfading effects in the communication channel. Fast fading is a known andgenerally undesirable phenomenon caused by the signal arriving at areceiver via a number of different paths. Therefore, in order to achievemaximum up-link capacity in a CDMA system, fast power control loops arerequired.

An inner power control (PC) loop is provided to adjust a UE'stransmission power to counter the so-called “near-far” problem. Theinner power control loop adjusts the transmission power of eachconnection such that the received signal power observed at the Node B issufficient to meet a particular quality of service (QoS) requirement ofeach particular connection; thereby reducing interference to others inthe system. The inner PC loop adjusts the UE's transmission power inorder to keep the received reverse link signal-to-interference ratio(SIR) as close to constant as possible.

The predetermined threshold, to which the inner loop SIR measure iscompared, is generated by the outer, quality-driven, power control loop.This loop sets a target SIR threshold that is proportional to therequired quality of service (QoS) for a given connection (usuallydefined in terms of target bit error rate (BER) or frame erasure rate(FER)). This target will vary as propagation conditions change, forexample as a function of a UE's speed and its specific propagationenvironment, as both have a major impact on the SIR required at the NodeB to maintain the desired QoS.

A reduction in interference is therefore desirable and, from asystem-wide perspective, power control can therefore be used in order tomaximise the system capacity. If the allocation of power amongst usersis carefully managed so as to provide only ‘just enough’ signal qualityat the receiving end then intercell interference power will be minimisedsince too much quality effectively equates to too much power and hencereduced capacity.

Power control can also be employed from a pure link-level-performanceperspective in order to mitigate the detection impairments causedthrough temporal variations in received signal power as a result of themobile radio propagation channel. If these variations can be removed viaeffective power control then the required mean SIR at the receiver,necessary to attain a certain bit or block error rate, can be shown tobe less than would be required in a fading channel without powercontrol. Thus, if every user can then operate at a lower SIR, systeminterference is reduced and system capacity is again increased.

Effective power control therefore constitutes an important aspect ofoverall system design for high-capacity spectrally efficient CDMAdeployments.

The power required of a transmitter in order to attain a certain radiolink quality (in terms of bit error- or block error rate) is a functionof four primary variables:

-   -   (i) The pathloss between transmitter and receiver;    -   (ii) The degree and performance of the error correction (channel        coding) scheme employed;    -   (iii) The prevailing channel propagation conditions (e.g. speed,        multipath); and    -   (iv) The data rate transmitted.

Power control is normally employed to track changes in (i)-pathloss and(iii)-channel propagation conditions, since these processes are notunder the control of the system operator. However, the degree of errorprotection and the data rate transmitted are under control of the systemoperator and this will affect the required amount of transmitted power.

The preferred embodiment of the present invention is described withregard to implementation on the UMTS Radio Access Network (UTRAN)protocol architecture 100, an overview of the pertinent portions ofwhich is described with regard to FIG. 1. The focus of the preferredembodiment of the invention relates to communication between the mediumaccess layer (MAC) (Layer-2) 110 and the physical layer (PHY) (Layer-1)over transport channels, which are the channels over which data iscommunicated between the MAC 110 and the PHY. The UMTS Radio AccessNetwork (UTRAN) protocol architecture at layer-2 utilises the concept ofTransport Channels 140, 142, 144 to control the bit rate and the forwarderror correction (FEC) scheme that is employed.

Transport Channels 140, 142, 144 may contain one or more TransportFormats 150, 152, 154, 156, 158, 160 that are characterised by twoparameter sets:

-   -   (i) A semi-static part that is associated with the Transport        Channel to which it belongs. This parameter set defines the type        of channel coding to be used, the Transmission Time Interval        (TTI), the Static Rate Matching Attribute, and the cyclic        redundancy code (CRC) length.    -   (ii) A dynamic part that is specific to the Transport Format.        This parameter set defines the Transport Block size and the        Transport Block Set Size, which is equal to the Transport Block        Size multiplied by the number of Transport Blocks to be        transmitted within the TTI.

Thus, all Transport Formats 150, 152, 154, 156, 158, 160 within the sameTransport Channel 140, 142, 144 inherit the same semi-static part,though each of those formats 150, 152, 154, 156, 158, 160 may have adifferent dynamic part. Transport Formats are identified by labelstermed Transport Format Indicators (TFIs).

Coded Composite Transport Channels (CCTrCHs) may be formed bymultiplexing one or more Transport Channel processing chains within amuiltiplexer 170 within Layer-1. The multiplexed output is mapped to anamount of physical resource 180, and in this manner, multiple TransportChannels may be multiplexed onto the same physical resource. Thiscombination of Transport Formats (TFIs) is termed a Transport FormatCombination (TFC).

The set of valid TFCS (as configured by layer-3) is termed a TransportFormat Combination Set (TFCS) and is notified to the MAC 120.Furthermore, the set of allowed TFCS within the TFCS might be restrictedbased on factors such as:

-   -   (i) The Puncturing Limit (PL), as set by Layer 3;    -   (ii) The amount of physical resource allocated 125; and    -   (iii) The amount of transmission power required for the TFC.

Higher layers, or lower layers, than the MAC layer 110, may impose theserestrictions 130. Either way, the MAC 110 is informed of the TFCSrestrictions 130. The MAC 110 in both the radio network controller (RNC)and the user equipment (UE) is then wholly responsible for selection ofa TFC from within the resulting allowed set. The selection of a TFC fromwithin this allowed set is generally based on optimisation of the datavolume to be transmitted within the constraints of the physical resourceallocated. Selection or changing of the current TFCS is managed byhigher layers (L3).

Typically, all TFCs within a TFCS require nominally the same signalquality to attain a given bit or block error rate. Layer-3 makesdecisions on the TFCS to use, based on information gathered frommeasurement reports or other metrics. Adjustment of the transmissionrate, per physical resource unit, is therefore primarily governed byLayer-3 decisions via appropriate selection of TFCS. This is shown byTFC selection control function 135 within the MAC layer, with TFCselection control input 138 to the Transport channel formatting withinLayer-1.

As the amount of error protection in transmissions is reduced, so theavailable information rate is increased, since fewer parity (orredundancy) bits must be transmitted. However, as the error protectionscheme is weakened, so the received energy per bit (E_(b)), relative tothe receiver noise spectral density (N₀) required to achieve a certainerror rate, will increase. Hence, the required transmit power will alsoincrease, which is known as a reduction in the coding gain.

The received signal power (S) is:S=E_(b)*R  [1]

where R is the information rate in bits/sec.

The noise power (N) is:N=N₀*W  [2]

where W is the receiver bandwidth in Hz.

Hence, the received signal to noise power ratio is simply:

$\begin{matrix}{\frac{S}{N} = {\frac{E_{b}}{N_{0}} \times \frac{R}{W}}} & \lbrack 3\rbrack\end{matrix}$

It can be seen from equation [3] that the required received signal tonoise ratio to achieve a certain E_(b)/N₀ increases linearly with thebit rate R (given a fixed system bandwidth W). However, the E_(b)/N₀required to achieve a certain block error rate is a function of the typeand amount of coding used and of the prevailing propagation channelconditions.

Thus, as less error protection is applied to a signal, the requiredtransmit power increases for two reasons:

-   -   (i) The coding gain is less (higher E_(b)/N₀ is required for a        given error rate); and    -   (ii) The information rate (R) is increased, from say, 100        kbits/sec to 200 kbits/sec.

Appropriate selection of the transmission rate (TFCS) is thereforetightly coupled with the power control scheme, since both direct powercontrol and selection of TFCS will affect the transmitted power, andthereby the system capacity. Since power is the shared resource in CDMAsystems, TFCS must be tightly managed, in conjunction with powercontrol, in order to maximise system capacity.

When the node-B transmits at full power, many UEs in favourable celllocations will see large values of carrier signal to noise plusinterference (C/(N+I)), resulting in excessive (too good) quality forthose UEs. Excess quality is undesirable from a network capacityperspective since it implies that unnecessary interference is beinginjected into the system, or conversely that a sub-optimal data rate isobtained for the transmit power being used.

Two mechanisms can be used to reduce this excess quality:

-   -   (i) Reduce the power transmitted to UEs operating with excess        C/I (i.e. use downlink power control). In this case, the data        rate per code to the UE will stay the same. The quality target        of the link is still maintained although the amount of        interference to other cells is reduced.    -   (ii) Decrease the processing gain available to those UEs by        increasing the bit rate per code. This is achieved by reducing        the amount of forward error correction (FEC) protection applied        to the data, before transmission. A number of TFCSs may be        employed for this purpose, each having varying degrees of FEC        protection. In this case, the data rate to the UE is increased,        the quality target is still attained, but the amount of        interference generated is not reduced since the power of the        transmission has not been reduced.

This link between power control and transport format selection isillustrated in FIG. 2, where a selection of transport format is made,from a number of variable transport formats 230, 240, 250 based on theavailable carrier to interference (C/I) 210. The C/I required for thelow rate 230, medium rate 240 and high rate 250 leaves correspondingvarious attenuation levels 235, 245 that can be imparted onto thetransport formats using power control. As shown, as an example, for ahigh rate transport format 250, there is no room for attenuation bypower control 220 to achieve a reduction in C/I 210.

Hence, in order to provide a transport format that would serve ato-be-transmitted packet data transmission 215 as shown, the medium ratetransport format 240 would be selected as this delivers the highest datarate for the C/I available 245. The highest rate transport format 250 isunavailable whereas the lowest rate transport format providessub-optimal data rate 230 for the available C/I 235. The inventor of thepresent invention has recognised that slow measurement report-basedpower control is less than adequate for shared channels.

In general, for shared packet data-based systems it is thereforepreferable to maintain full, or close to full transmit power from thenode-B whilst maximising the data rate to each user since for datavolumedriven applications such as web-browsing and file-transfer, every userbenefits from every other user receiving the best data rate possible, atany particular moment in time. This is because physical channel resourceis liberated and may be used by other users.

In summary, the 3GPP specifications assume a downlink shared channel(DSCH) call model that allows for the implementation of slowmeasurement-report-based power control of Physical Downlink (DL) SharedChannels (PDSCHs). In such a scheme, the user equipment (UE) isrequested to send measurement reports from which the current meanpathloss between node-B and UE may be determined. In addition, the UEmay send interference power measurements. This DL power control schemeis termed “slow” due to the delay in the UE making the measurement andconveying this to the RNC entity via the node-B.

As the PC scheme is relatively slow, it provides a less than optimalsolution in PDSCHs. This results in increased interference andsub-optimal use of the available communication resource.

A need therefore exists, in general, for an improved power controlarrangement and method of operation, and in particular, an arrangementand method for improved downlink power control for shared channels in anUTRA-TDD system, wherein the above-mentioned disadvantages may bealleviated.

STATEMENT OF INVENTION

In accordance with a first aspect of the present invention, there isprovided a method for setting a power control level in a wirelesscommunication system, the method comprising the steps of:

-   -   obtaining transmission information from a wireless subscriber        unit;    -   modifying a power control level in response to said transmission        information; and    -   modifying a communication channel format in response to said        transmission information.

In accordance with a second aspect of the present invention, there isprovided a method for selecting a transport format to transmit messagesin a wireless communication system, the method comprising the steps of:

-   -   obtaining transmission information from a wireless subscriber        unit; and    -   modifying a communication channel format in response to said        transmission information.

In accordance with a third aspect of the present invention, there isprovided a method for setting a power control level, the methodcomprising the step of:

-   -   extracting a portion of a power control signal;    -   using said portion of a power control signal to determine a        signal quality granularity adjustment to transmit a signal in        accordance with a number of communication channel formats; and    -   selecting a downlink transmission rate or power control level in        response to said determined signal quality granularity.

In accordance with a fourth aspect of the present invention, there isprovided a wireless communication unit adapted to incorporate the methodsteps of the first or second aspect above.

In accordance with a fifth aspect of the present invention, there isprovided a wireless communication system adapted to incorporate themethod steps of the first, second or third aspect above.

In accordance with a sixth aspect of the present invention, there isprovided a radio network controller comprising:

-   -   means for obtaining measurement report data from a wireless        subscriber unit;    -   means for determining a downlink transmission rate or power        control level based on said measurement report data; and    -   means for modifying a downlink transmission rate or power        control level in response to said measurement report data by        modifying a communication channel format.

In accordance with a seventh aspect of the present invention, there isprovided a storage medium storing processor-implementable instructionsfor controlling a processor to carry out the method of the first, secondor third aspect above.

In summary, a method and apparatus for setting a power control level, adownlink transmission rate, or a transport channel format in a wirelesscommunication system is described. The method and apparatus usetransmission information, preferably re-transmission requestinformation, obtained from a wireless subscriber unit; determine adownlink transmission rate or power control level based on thetransmission information; and modify a downlink power control level andselecting a communication channel format in response to the transmissioninformation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a known transport channel architecture for a UTRATDD-CDMA communication system;

FIG. 2 illustrates a known association between rate control andtransport format for a UTRA TDD-CDMA communication system;

Exemplary embodiments of the present invention will now be described,with reference to the accompanying drawings, in which:

FIG. 3 shows a block diagram of a communication system adapted tosupport the various inventive concepts of a preferred embodiment of thepresent invention;

FIG. 4 shows an architectural block diagram of an RNC-Node B-UEcommunication arrangement, adapted in accordance with various inventiveconcepts of a preferred embodiment of the present invention;

FIG. 5 shows a state diagram of down link transmissions, adapted inaccordance with the preferred embodiment of the present invention; and

FIG. 6 shows a flowchart of a downlink shared channel power controloperation according to the preferred embodiment of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In summary, the preferred embodiments of the present invention relate toa power control scheme and/or a scheme for modifying a transmission ratefor use in downlink-shared channels in a non fast-fading environment.The concept of rate adaptation is used in order to offer the bestpossible data rate to all users, at any particular moment in time. Inparticular, RLC-based information from a UE, indicating on a frequentbasis a failure rate of packet data transmissions, is used to select atransport format. The transport format is selected to provide a powerlevel window, with power control and/or rate adaptation used to optimisetransmission levels within such window(s).

Hence, as a user equipment moves within a cell, causing the UE's carrierto interference levels to change rapidly, frequent transmission from theUE are used to continually select an optimal transport format, with DLpower control and/or rate adaptation used as a fine-tuning processwithin each transport format to further optimise carrier to interferencelevels. The rate adaption is implemented by modifying a transportformat. The invention is targeted at increasing the overall capacity ofdownlink shared channels in UTRA TDD. These channels are typicallyallocated and used sporadically by users on the system, and as such, therequirements for power control are somewhat different to those fordedicated physical channels.

In the context of the present invention, the use of a transport formatcombination set, applicable to UMTS-based communications systems isdescribed. It is within the contemplation of the invention that the term‘transport format’ in this context encompasses certain attributes of abearer that relate to Layer 1 of a communication system. It is alsowithin the contemplation of the invention that the fine-tuning ofcarrier to interference levels may be performed by power control and/orrate adaptation and/or any other known means to those skilled in theart. Henceforth, the expression ‘power control’ should be considered asencompassing all such operations.

Referring now to FIG. 3, a cellular-based telephone communication system300 is shown in outline, in accordance with a preferred embodiment ofthe invention. In the preferred embodiment of the invention, thecellular-based telephone communication system 300 is compliant with, andcontains network elements capable of operating over, a UMTSair-interface. In particular, the invention relates to the ThirdGeneration Partnership Project (3GPP) specification for wide-bandcode-division multiple access (WCDMA) standard relating to the UTRANradio Interface (described in the 3G TS 25.xxx series ofspecifications).

A plurality of subscriber terminals (or user equipment (UE) in UMTSnomenclature) 312, 314, 316 communicate over radio links 318, 319, 320with a plurality of base transceiver stations, referred to under UMTSterminology as Node-Bs, 322, 324, 326, 328, 330, 332. The systemcomprises many other UEs and Node Bs, which for clarity purposes are notshown.

The wireless communication system, sometimes referred to as a NetworkOperator's Network Domain, is connected to an external network 334, forexample the Internet. The Network Operator's Network Domain (describedwith reference to both a 3^(rd) generation UMTS and a 2^(nd) generationGSM system) includes:

-   -   (i) A core network, namely at least one Gateway GPRS Support        Node (GGSN) 344 and or at least one Serving GPRS Support Nodes        (SGSN); and    -   (ii) An access network, namely:    -   (ai) a GPRS (or UMTS) Radio network controller (RNC) 336-240; or    -   (aii) Base Site Controller (BSC) in a GSM system and/or    -   (bi) a GPRS (or UMTS) Node B 322-232; or    -   (bii) a Base Transceiver Station (BTS) in a GSM system.

The GGSN/SGSN 344 is responsible for GPRS (or UMTS) interfacing with aPublic Switched Data Network (PSDN) such as the Internet 334 or a PublicSwitched Telephone Network (PSTN) 334. A SGSN 344 performs a routing andtunnelling function for traffic within say, a GPRS core network, whilsta GGSN 344 links to external packet networks, in this case onesaccessing the GPRS mode of the system.

The Node-Bs 322-232 are connected to external networks, through basestation controllers, referred to under UMTS terminology as Radio NetworkController stations (RNC), including the RNCs 336, 338, 340 and mobileswitching centres (MSCs), such as MSC 342 (the others are, for claritypurposes, not shown) and SGSN 344 (the others are, for clarity purposes,not shown).

Each Node-B 322-332 contains one or more transceiver units andcommunicates with the rest of the cell-based system infrastructure viaan I_(ub) interface, as defined in the UMTS specification.

Each RNC 336-240 may control one or more NodeBs 322-332. Each MSC 342provides a gateway to the external network 334. The Operations andManagement Centre (OMC) 346 is operably connected to RNCs 336-340 andNode-Bs 322-232 (shown only with respect to Node-B 326 for clarity). TheOMC 346 administers and manages sections of the cellular telephonecommunication system 300, as is understood by those skilled in the art.

In the preferred embodiment of the invention, one or more RNCs 336, 338,340 and/or corresponding Node-Bs 322-332 have been adapted to providedownlink power control by selecting and utilising an appropriatetransport format combination set (TFCS). In particular, the preferredembodiment of the present invention describes a mechanism for adaptingDL power control using DL error statistics and/or measurement reports onpathloss and interference. With such information, a more RNC, forexample RNC 336, is able to make a decision on whether to increase ordecrease the data rate and/or adjust a gain or attenuator in atransmitter chain to reflect a power control of a communication to a UE312, via changing the Transport Format Combination Set (TFCS).

The DL power control and TFCS selection function 348 indicates to theNode B 322, over the Iub interface, the selected TFCS and correspondinggain control for transmissions to the UE 312. In response to thisindication, the Node B 322 adjusts a variable gain element 445 that setsthe power control levels of its wireless transmissions.

The various components within the RNC 336 are realised in thisembodiment in integrated component form. Of course, in otherembodiments, they may be realized in discrete form, or a mixture ofintegrated components and discrete components, or indeed any othersuitable form. Furthermore, in this embodiment the power control TFCSselection function 348 is implemented preferably in a digital signalprocessor. However, it is within the contemplation of the invention thatthe power control TFCS selection function 348 described in the aboveembodiments can be embodied in any suitable form of software, firmwareor hardware. The power control TFCS selection function 348 may becontrolled by processor-implementable instructions and/or data, forcarrying out the methods and processes described, which are stored in astorage medium or memory.

The processor-implementable instructions and/or data may include any ofthe following:

-   -   (i) Transmission rate and/or power control algorithms;    -   (ii) Transmission rate and/or power control thresholds; and    -   (iii) Transmission rate and/or power control equations.

The memory can be a circuit component or module, e.g. a random accessmemory (RAM) or a form of programmable read only memory (PROM), or aremovable storage medium such as a disk, or other suitable medium.

It is also envisaged that for other wireless communication systems,other criteria and algorithms or equations could be employed indetermining an appropriate power control scheme and/or transmissionrate. Such schemes would still benefit from the concept of using statusinformation or measurement reports in order to select a transport formatthat maximise the use of the available data rate, whilst maintaining anacceptable error performance.

It is also within the contemplation of the invention that suchadaptation of the physical layer (air-interface) elements may bealternatively controlled, implemented in full or implemented in part byadapting any other suitable part of the communication system 300. Forexample, elements involved in determining or facilitating a transmissionrate or power control level, such as base site controllers, basetransceiver stations (or Node Bs), intermediate fixed communicationunits (for example repeaters) in other types of systems may, inappropriate circumstances, be adapted to provide or facilitate the powercontrol features as described herein.

Referring now to FIG. 4, a system block diagram, with indications on thesignalling information passing between various components, isillustrated in accordance with the preferred embodiment of the presentinvention.

The signalling information predominantly passes between the radionetwork controller 336 and one or more UE 312, via the Node B 322serving the respective UE 312. The RNC 336 is shown, for claritypurposes, as being divided into a radio link control layer (RLC) 405 anda radio resource control layer (RRC) 425. Similarly, the UE 312 isshown, for clarity purposes, as being divided into a radio link controllayer (RLC) 470 and a radio resource control layer (RRC) 480, withregard to signalling information. Such layering of a communications iswell known in the art, and further described with respect to the 7-layerOSI protocol, see 3GPP TS25.301.

In accordance with the current 3GPP standard, the vast majority ofpackets sent on a downlink channel are sent 450 from the RLC layer 405of the RNC 336 in a RLC acknowledged mode (AM), to facilitatere-transmission in the event that the packet is lost over the airinterface.

The UE 312 is requested to send a radio link control (RLC) statusprotocol data unit (PDU) 465 indicating which packets have been receivedcorrectly and which have been lost. Such a request is made by settingthe poll bit in the RLC message header 440. Hence, after performing acyclic redundancy check (CRC) on the AM dedicated traffic channel (DTCH)PDUs, a determination of the poll bit notification 475 can be made. TheUE 312 then transmits a RLC status PDU 465 in response to the pollinitiated by its respective RNC 336.

From this information, the RNC 336 is able to estimate the currentdownlink block error rate (BLER), as observed by the UE 312. Inaccordance with the preferred embodiments of the present invention, suchBLER information of the downlink-shared channel (DSCH) 410 is input to aDL power control and TFCS selection function 348.

When appropriate, the DL power control and TFCS selection function 348may decide to supplement such information with measurement reports. Assuch, the DL power control and TFCS selection function 348 has a controlinput 420 to the RRC layer 425 of the RNC 336. In response to a requestfrom the DL power control and TFCS selection function 348, the RRC layer425 of the RNC 336 may transmit a measurement control request 490 to theRRC layer 480 of the UE 312. The RRC layer 480 of the UE 312 transmits ameasurement report 485 back to the RRC layer 425 of the RNC 336, whichis forwarded 430 to the DL power control and TFCS selection function348.

Hence, by utilising DSCH error statistics, in conjunction withmeasurement reports 465 on pathloss and interference, the RNC 336 isable to make a decision on whether to increase or decrease the data rateto the UE 312, by modifying the Transport Format Combination Set (TFCS).

The DL power control and TFCS selection function 348 indicates 435 tothe Node B 322, over the Iub interface, the selected TFCS andcorresponding gain control for PDSCH transmissions to the UE 312. Inresponse to this indication, the Node B 322 adjusts a variable gainelement 445 setting the power control levels of its wirelesstransmissions.

The differences between the typical carrier to interference (C/I) levelsrequired for each TFCS are preferably known a priori and are stored inthe RNC as SIR_(j). Two variables are also preferably stored in the RNC:

-   -   (i) The current TFCS; and    -   (ii) The current attenuation per code from cell reference power        (A_(n)).

The currently used TFCS is dynamically indicated to the UE 312 via RRCsignalling within the Physical Shared Channel Allocation Message(PSCHAM). Upon a decision to change the power per code delivered to theUE 312 by an amount A (as the result of newly-received measurementinformation, or newly-determined BLER information), the followingprocess is executed for each j^(th) TFCS: —A _(n+1,j) =A _(n)+Δ+(SIR_(i)−SIR_(j))  [4]

Equation [4] effectively calculates the attenuation from the maximumallowable per-code power (usually equal to a cell reference or PrimaryCommon Control Physical Channel (P-CCPCH) power) that would be requiredwhen switching to using TFCS j, given the current attenuation (A_(n)),the current TFCS (i), the required power step (Δ) and the differences inSIR between TFCS i and TFCS j.

The TFCS with the smallest positive attenuation A_(n+1,j) is selected asthe TFCS that may provide a maximum data rate to the UE whilst notviolating the maximum per-code power restriction.

It is envisaged that Δ may be derived in several ways:

-   -   (i) Directly from the RLC layer in the RNC which is receiving        RLC status reports on the error performance of the downlink        acknowledged mode transmissions, or via BLER measurement reports        signalled to RNC by the UE; or    -   (ii) From pathloss and interference measurement reports        signalled from a UE to RNC; or    -   (iii) A combination of the above two schemes.

Furthermore, the inventive concepts of the present invention utilisemethods to handle the sporadic data transfer that is characteristic ofdata-call sessions using shared channels. Pauses in transmission causesubsequent pauses in RLC (or other measurement report-based) BLERinformation since there is little or no transmitted data to be reportedon. As such, it is within the contemplation of the invention that powercontrol may be driven by pathloss and interference-based measurementreports only. However, it is noted that such measurement reports consumevaluable uplink resource, which is wasted in the absence of downlinktraffic to control. Although it is known for DL PC in PSCHAM to use suchmeasurement reports, it is hereby proposed to use the ‘measurementreport only’ option to adjust TFCS (in contrast to PC) only when thereis little traffic to drive the RLC-based PC scheme.

Therefore, in a further embodiment of the present invention, the notionof a “quiet timer” is utilised. The quiet timer is reset and re-startedwhenever downlink RLC buffer volumes exceed a certain thresholdindicating that significant downlink resource is required. When asubstantial use of a downlink resource is required, it is obviouslydesirable to employ power and rate control to maximise throughput. Oncethe RLC buffer occupancy falls to, or below, a particular threshold, orif the number of PDUs being reported within RLC status reports is belowa certain level, for a period of, say, Q ms, it is decided that notenough data volume exists to warrant power/rate-controlled transmissions(which may require significant use of uplink resource). Additionally theincoming error statistics may also be too infrequent or inaccurate to beof use. In this scenario, power control and rate adaptation is switchedoff until it is determined worthwhile to re-start the procedure.

This is especially useful when the system is used for typicalweb-browsing applications. This will normally result in periods ofdownlink activity during HTTP page download, followed by periods ofdownlink inactivity (while the user digests the information onscreen).

In accordance with the preferred embodiment of the present invention, itis desirable for the downlink power control scheme to utilise a numberof logical states, as described below with respect to FIG. 5. In FIG. 5,a state diagram 500 is shown in accordance with the preferred embodimentof the present invention. The state diagram 500 represents a downlinkpower control scheme that utilises three logical states:

-   -   (i) DLPC_Invalid state—505;    -   (ii) DLPC_Off state—535    -   (iii) DLPC_Valid state 515.

Transition between the three states is preferably driven by any of anumber of parameters:

-   -   (i) DL RLC buffer occupancy and associated thresholds,    -   (ii) Measurement report information from the UE, and    -   (iii) On the ‘quiet-time’ timer T_(Q).

A first state—a DLPC_Invalid state—505 is employed when it is desirableto utilise adjustment of power control, but the required information hasyet to be gathered or is deemed ‘out-of-date’. This may happen followingan appreciable pause in downlink transmission. In this DLPC_Invalidstate 505, initial power control settings must first be establishedbased upon measurement information as measured at the UE, as shown instate transition step 510. The initial power control settings need to bereported to UTRAN before power/rate controlled downlink shared channelallocation can be granted.

However, in order to avoid an increase in system latency, before ameasurement report has been received, downlink shared channelallocations may still be granted. However, they preferably use thelowest-rate TFCS and the attenuation must be set to the minimumallowable.

A DLPC_Invalid State 505 Transition 510 to a DLPC_Valid State 515

For the DL power control scheme to transition 510 from a DLPC_Invalidstate 505 to DLPC_Valid state 515, measurement information must beextracted from the UE. This is due to the fact that any previous powercontrol information, from a previous power control adjusted downlinkshared channel (DSCH) session, is deemed to be invalid due to the lengthof the intervening time period. Measurement report information mayarrive at the RNC as the result of either:

-   -   (i) A UE-initiated process (via various UL messages) or    -   (ii) As the result of a direct UTRAN measurement report request        sent for the explicit purposes of downlink power control.        (a) UE-Initiated Transition to DLPC_Valid State 515

Examples of UE-initiated UL messages, in which the relevant measurementreport information may be contained, are listed below in Table 1.

TABLE 1 PCCPCH Timeslot RRC Message RSCP ISCP CellUpdate ✓ ✓InitialDirectTransfer ✓ ✓ PUSCHCapacityRequest ✓ ✓RRCConnectionReEstablishmentRequest ✓ ✓ RRCConnectionRequest ✓ ✓UplinkDirectTransfer ✓ ✓

The above Layer-3 messages are examples of messages that are initiatedby the UE that can be used to carry additional measurement information(RSCP and ISCP).

Each time measurement report information is received from the UE, andthe DL power control scheme is in the DLPC_OFF state 535 or DLPC_Invalidstate 505, a transition to a DLPC_Valid state 515 is enabled and timerT_(Q) is reset and started.

In particular, a Physical Uplink Shared Channel (PUSCH) Capacity Requestmessage from a UE to UTRAN may optionally contain P-CCPCH receivedsignal code power (RSCP) and a list of Interference Signal Code Power(ISCP) values for specified timeslots. In this model, a UE that has beendormant for a period, but has maintained an RRC connection, sends aPUSCH capacity request to the RNC. It could be expected that downlinktransmission would follow shortly after this. As such, by includingPCCPCH RSCP and Timeslot ISCP information in a PUSCH Capacity RequestMessages, immediate power control can be enabled on the resultant DSCH.

(b) UTRAN-Initiated Transition to a DLPC_Valid State 515

In the event that there is sufficient downlink data for a UE to be sentvia a DSCH and the power control process is in the DLPC_Invalid state505, an explicit measurement report request must be signalled to the UEin order to initiate the downlink power control process. To achievethis, a Measurement Control message must be sent from UTRAN to the UE inorder to retrieve a Measurement Report message from the UE.

It is noteworthy that PDSCHs that are not power control or transmissionrate adjusted may still be employed during this period using thelowest-rate TFCS available with minimum attenuation.

DLPC_Valid State 515 Returning (Transition 520) to a DLPC_Valid State515

The DLPC_Valid state is retained so long as RLC status informationpertaining to N>=N_(Q) PDUs arrives at the RNC 336,

where:

N=is a counter; and

N_(Q) is a minimum threshold value put in place in order to prevent theloop adjusting the power to a UE from which sufficiently reliable PDUerror statistics have not been received.

Furthermore, the DLPC_Valid state 515 is only maintained if the quiettimer T_(Q) has not expired. The quiet timer, denoted T_(Q), is used todetermine the duration of this allowable ‘quiet’ period. Optionally, thetimer may be continuously reset to maintain (transition 520) the DLpower control scheme in a DLPC_Valid state 515. A timer T_(Q) reset maybe based on a number or frequency of PDU reported information and/orbased on the DL PLC buffer volume and thresholds.

A DLPC_Valid State 515 Transition 525 to a DLPC_Invalid State 505

A DLPC_Valid state 515 transitions to a DLPC_Invalid state 505 occurswhen the timer T_(Q) expires. The measurement reporting process forP-CCPCH RSCP and timeslot ISCP may (optionally) be terminated at thispoint to conserve UL physical resource. This may be performed using, forexample, the Measurement Control RRC message.

DLPC_OFF State 535 Transition 540 to the DLPC_Invalid State 505

A DLPC_OFF state 535 is employed for downlink transmissions that do notuse power control. If the DL power control scheme is in a DLPC_OFF state535, no action need be taken to transition from the DLPC_OFF state 535to the DLPC_Invalid state 505. Any transition is based purely on adesire to perform a power control adjustment operation on a downlinkshared channel transmission. Such an indication to transition may bebased on the DL RLC buffer volume or, for example, when transitioningfrom a fast access channel (FACH) mode to a DSCH mode.

As shown, in order to enter the DLPC_Valid state 515, the process musttransition from the DLPC_OFF state 535 via the DLPC_Invalid state 505into the DLPC_Valid state 515 before power control on DSCH can beperformed. This ensures that recent measurement report information isobtained, in order that a good estimate as to the initial transportformat rate and the initial required attenuation may be made.

The TFCS selection algorithm, used in the preferred embodiment of thepresent invention, employs the following equation:Avail_(j)={(PCCPCH_RSCP−Timeslot_ISCP)−SIR_(j) −K _(PDSCH)}≧0  [5]

-   -   where the parameters used to determine the initial TFCS and        attenuation are:    -   (i) PCCPCH RSCP—Received Signal Code Power of the P-CCPCH beacon        physical channel. This parameter is signalled by a UE in a        measurement report.    -   (ii) Timeslot ISCP—Interference Signal Code Power of a specified        timeslot. This parameter is signalled by a UE in a measurement        report.    -   (iii) SIR_(j)—A nominal target SIR per code for TFCS j. This        parameter is known α priori and stored at the RNC.

(iv) K_(PDSCH)—A constant value, which is configurable within the RNC.This parameter is used to provide a conservative margin on the initialTFCS and attenuation values selected.

Once the above parameters are known to the RNC, each TFCS is tested tosee whether it is available using equation [5].

The highest rate TFCS (j=i) for which Avail_(j) is TRUE in equation [5],is then selected.

The initial attenuation used per code (relative to P-CCPCH transmit codepower) is calculated as: —A _(0,i)=PCCPCH_RSCP−Timeslot_ISCP−SIR_(i) −K _(PDSCH)  [6]

Referring now to FIG. 6, a flowchart 600 of the DL power control schemeaccording to the preferred embodiment of the present invention isillustrated. It is assumed that the DL power control scheme willcommence in a DLPC_OFF state, as shown in step 605. If the operatingconditions change such that a power controlled DSCH is required, in step610, a transition occurs to a DLPC_Invalid state, as shown in step 615.

If a recent measurement report has been received from the UE, in step620, the quiet timer T_(Q) is reset in step 630. If a recent measurementreport has not been received from the UE, in step 620, then ameasurement control message is transmitted from the UTRAN to the UE tosolicit a measurement from the UE, as shown in step 625.

When a UE measurement report has been received in step 620, the schemetransitions to a DLPC_Valid state 670. Appropriate parameters forcalculating equation [4] are extracted and a calculation of the initialDSCH TFCS to use is made. Furthermore, a calculation is made on theinitial attenuation level to use, in equation [5], as shown in step 635.

A determination is then made as to whether the quiet timer T_(Q) hasexpired in step 640. If the quiet timer T_(Q) has expired in step 640, atransition of the power control scheme to a DLPC_Off state occurs, asshown in step 610. If the quiet timer T_(Q) has not expired in step 640,a determination is made as to whether the RLC-status PDU information hasarrived, in step 645. If the RLC-status PDU information has not arrivedin step 645, a PDSCH is sent at the current power setting, as shown instep 650, and the quiet timer T_(Q) checked in a loop back to step 640.

If the RLC-status PDU information has arrived in step 645, adetermination is made as to whether N>=N_(Q) PDUs, in step 655. If it isdetermined that N>=N_(Q) PDUs, in step 655 has not been satisfied, aPhysical Downlink Shared Channel (PDSCH) is sent at the current powersetting, as shown in step 650, and the quiet timer T_(Q) checked in aloop back to step 640.

If it is determined that N>=N_(Q) PDUs, in step 655 has been satisfied,an iteration of the power adjustment loop is performed, as shown in step660. The current power setting is then updated, and the quiet time T_(Q)and N values are reset. A PDSCH is then sent at the current powersetting, as shown in step 650, and the quiet timer T_(Q) checked in aloop back to step 640. The DLPC_Invalid state 670 is then maintaineduntil the quiet timer T_(Q) has expired in step 640, whereby atransition of the power control scheme to a DLPC_Off state occurs.

It will be understood that the method and arrangement for open-looppower control described above provides at least the followingadvantages:

-   -   (i) The TFCS that provides the maximum data rate to the UE is        selected, whilst not violating the maximum per-code power        restriction.    -   (ii) Implementation of this invention allows standards        compliance to be retained.    -   (iii) Minimises the signalling overhead.

Hence, the aforementioned method and arrangement for providing powercontrol substantially negates at least the problems associated with theupdate rate limitations of the PC scheme in an UTRA-TDD CDMA wirelesscommunication system.

Thus, a configuration and method for effecting power control or adaptingtransmission rates in a wireless communication system has been describedwherein the aforementioned disadvantages associated with prior artarrangements has been substantially alleviated. Whilst specific, andpreferred, implementations of the present invention are described above,it is clear that one skilled in the art could readily apply variationsand modifications of such inventive concepts.

1. A method for downlink transmission in a wireless communicationsystem, the method comprising, at a base station or radio networkcontroller: obtaining transmission status information, with respect todownlink transmissions, from a wireless subscriber unit, wherein thetransmission status information comprises at least one of measurementson pathloss and error performance on the downlink transmissions;selecting a transport format to be used in a transmission based at leastin part on the transmission status information; modifying a downlinktransmit power level of the transmission or adapting a transmission datarate of the transmission, based at least in part on the selectedtransport format; and periodically obtaining further transmission statusinformation and selecting a transport format for downlink transmissionbased at least in part on the further transmission status information,wherein a period between obtaining transmission status information andfurther transmission status information is controlled by the basestation or the radio network controller.
 2. The method of claim 1further comprising calculating the transmission status information fromat least one status report of downlink transmissions received from thewireless subscriber unit.
 3. The method according to claim 1, whereinthe wireless communication system uses downlink shared channels.
 4. Themethod according to claim 1, wherein the transmission status informationincludes re-transmission requests from the wireless subscriber unit. 5.The method according to claim 1, wherein the transmission statusinformation includes one or more of the following: an error performanceindication of a downlink communication link; a downlink pathlossmeasurement report; and a downlink interference measurement report. 6.The method according to claim 5, wherein the transmission statusinformation includes the downlink pathloss measurement report signaledfrom the wireless subscriber unit to the radio network controller viathe base station.
 7. The method according to claim 5, wherein thewireless communication system supports a transmission between the basestation and the wireless subscriber unit, and wherein the transmissionstatus information includes the downlink pathloss measurement reportsignaled from the wireless subscriber unit to the base station.
 8. Themethod of claim 1, further comprising operating a downlink transmissionat a maximum power control level before modifying the downlink transmitpower level based at least in part on the selected transport format. 9.The method according to claim 1, wherein obtaining the transmissionstatus information includes one or more of: receiving the transmissionstatus information from the wireless subscriber unit as part of anuplink message that the wireless subscriber unit has determined totransmit; and requesting a measurement report from the wirelesssubscriber unit, and receiving measurement report data in response tothe request.
 10. The method according to claim 1, further comprising:iteratively obtaining further transmission status information from thewireless subscriber unit; determining a period of time betweeniterations; and initiating a request for receiving transmission statusinformation in response to the period of time exceeding a timethreshold.
 11. The method of claim 10, further comprising enabling anddisabling initiating of the request for receiving transmission statusinformation.
 12. The method of claim 1, wherein obtaining thetransmission status information further comprises one or more of:obtaining transmission status information from the wireless subscriberunit when the wireless subscriber unit determines to transmit an uplinkmessage; and requesting measurement report data from the wirelesssubscriber unit if optimization of downlink transmission power iscurrently active.
 13. The method according to claim 12, furthercomprising activating the optimization of downlink transmission powerwhen a number of data packets to be transmitted on a downlink channelexceeds a packet threshold amount.
 14. The method according to claim 12,further comprising activating the optimization of downlink transmissionpower when a predetermined quantity of transmission status informationhas been received.
 15. The method according to claim 1, furthercomprising switching off power control based on at least one of thefollowing: an amount of buffered down link data being less than or equalto a threshold value; and whether an elapsed time since reception of thetransmission status information has exceeded a time threshold value. 16.The method according to claim 1, further comprising selecting thetransport format with a smallest positive attenuation of a downlinktransmission.
 17. The method according to claim 1, further comprisingallocating uplink transmission resources to carry the transmissionstatus information from the wireless subscriber unit to the base stationif an amount of buffered downlink data exceeds a time threshold value.18. The method according to claim 17, further comprising releasing theuplink transmission resources and terminating the selection of thetransport format, and the modification of the downlink transmit powerlevel if the buffered downlink data is less than or equal to thethreshold value.
 19. A system for wireless data transmission,comprising: a radio resource controller configured to obtain ameasurement report, from a wireless subscriber unit, relating to one ormore of pathloss and interference for downlink transmissions to thewireless subscriber unit; and a radio network controller or base stationoperably coupled to the radio resource controller configured todetermine a downlink transmit power level or adapt a transmission datarate of a transmission, and to determine a transport format for atransmission to the wireless subscriber unit based at least in part onthe measurement report obtained from the wireless subscriber unit,wherein the radio resource controller periodically obtains furthermeasurement reports and the radio network controller or base stationdetermines the transport format for downlink transmission based at leastin part on the further measurement reports, and wherein the radionetwork controller or base station controls a period between obtainingthe measurement report and further measurement reports.
 20. The systemaccording to claim 19, further comprising determining the downlinktransmit power level and transport format based on at least one of thefollowing: an amount of buffered downlink data being less than or equalto a threshold value; and whether an elapsed time since reception of thetransmission status information has exceeded a time threshold value. 21.A computer-readable medium comprising program code for a wirelessdownlink data transmission, the program code for, at a base station orradio network controller: obtaining transmission status information,with respect to downlink transmissions, from a wireless subscriber unit,wherein the transmission status information comprises at least one ofmeasurements on pathioss and error performance on the downlinktransmissions; selecting a transport format to be used in a transmissionbased at least in part on the transmission status information; modifyinga downlink transmit power level of the transmission or adapting atransmission data rate of the transmission, based at least in part onthe selected transport format; and periodically obtaining furthertransmission status information and selecting a transport format fordownlink transmission based at least in part on the further transmissionstatus information, wherein a period between obtaining transmissionstatus information and further transmission status information iscontrolled by the base station or the radio network controller.
 22. Thecomputer-readable medium of claim 21, further comprising program codefor switching off power control and transport format selection based onat least one of the following: an amount of buffered downlink data to betransmitted to the wireless subscriber unit; and whether an elapsed timesince reception of the measurement reports has exceeded a time thresholdvalue.
 23. The computer-readable medium of claim 21, further comprisingprogram code for allocating uplink transmission resources to carry ameasurement report from the wireless subscriber unit to the base stationif an amount of buffered downlink data exceeds a threshold value. 24.The computer-readable medium of claim 23, further comprising programcode for releasing the uplink transmission resources and not modifyingthe power level and selecting the transport format, if the amount ofbuffered downlink data to be transmitted to the wireless subscriber unitdoes not warrant power and rate controlled downlink transmissions.
 25. Abase station for a wireless communication system, the base stationcomprising: a receiver configured to obtain transmission statusinformation, with respect to downlink transmissions, from a wirelesssubscriber unit, wherein the transmission status information comprisesat least one of measurements on pathloss and error performance on thedownlink transmissions; and a processor configured to select a transportformat to be used in a transmission based at least in part on thetransmission status information and modify a downlink transmit powerlevel of the transmission or adapt a transmission data rate of thetransmission, based at least in part on the selected transport format,wherein the receiver periodically obtains further transmission statusinformation and the processor selects a transport format for downlinktransmission based at least in part on the further transmission statusinformation, wherein a period between obtaining transmission statusinformation and further transmission status information is controlled bythe processor.
 26. A radio network controller for a wirelesscommunication system, the radio network controller comprising: areceiver configured to obtain transmission status information, withrespect to downlink transmissions, from a wireless subscriber unit,wherein the transmission status information comprises at least one ofmeasurements on pathloss and error performance on the downlinktransmissions; and a processor configured to select a transport formatto be used in a transmission based at least in part on the transmissionstatus information and modify a downlink transmit power level of thetransmission or adapt a transmission data rate of the transmission,based on the selected transport format, wherein the receiverperiodically obtains further transmission status information and theprocessor selects a transport format for downlink transmission based atleast in part on the further transmission status information, wherein aperiod between obtaining transmission status information and furthertransmission status information is controlled by the processor.
 27. Awireless subscriber unit for a wireless communication system, thewireless subscriber unit comprising: a transmitter configured totransmit transmission status information, with respect to downlinktransmissions, to a base station, wherein the transmission statusinformation comprises at least one of measurements on pathloss and errorperformance on the downlink transmissions; and a receiver configured toreceive a transmission from the base station at a downlink transmitpower level and using a selected transport format, wherein a transportformat for the transmission is selected based at least in part on thetransmission status information and the downlink transmit power level ofthe transmission is modified, or a transmission data rate is adapted,based at least in part on the selected transport format, wherein thetransmitter is further configured to periodically transmit furthertransmission status information wherein a period between transmittingtransmission status information and further transmission statusinformation is controlled by the base station or a radio networkcontroller.
 28. A method for receiving a downlink transmission, themethod comprising, at a wireless subscriber unit: transmittingtransmission status information, with respect to downlink transmissions,to a base station, wherein the transmission status information comprisesat least one of measurements on pathloss and error performance on thedownlink transmissions; and receiving a transmission from the basestation at a downlink transmit power level and using a selectedtransport format, wherein a transport format for the transmission isselected based at least in part on the transmission status informationand the downlink transmit power level of the transmission is modified,or a transmission data rate is adapted, based at least in part on theselected transport format, wherein the transmitting further includesperiodically transmitting further transmission status informationwherein a period between transmitting transmission status informationand further transmission status information is controlled by the basestation.
 29. A computer-readable medium comprising program code forreceiving a downlink transmission, the program code for, at a wirelesssubscriber unit: transmitting transmission status information, withrespect to downlink transmissions, to a base station, wherein thetransmission status information comprises at least one of measurementson pathloss and error performance on the downlink transmissions; andreceiving a transmission from the base station at a downlink transmitpower level and using a selected transport format, wherein a transportformat for the transmission is selected based at least in part on thetransmission status information and the downlink transmit power level ofthe transmission is modified, or a transmission data rate is adapted,based at least in part on the selected transport format, wherein thetransmitting further includes periodically transmitting furthertransmission status information wherein a period between transmittingtransmission status information and further transmission statusinformation is controlled by the base station.